1. Field
The present disclosure relates generally apparatus and methods for controlling idle mode in a wireless device, and more specifically to controlling access point or relay idle mode through controlled variation of the wake up duty cycles of the wireless device.
2. Background
Wireless communication deployment models are currently emerging where coverage and high capacity is enabled via dense networks of low-cost nodes. These nodes may be either wired access points (APs) or wireless relay stations (RS). Cost efficiency of such deployments is achieved not only due to low device cost but, more importantly, due to reduction in the costs of site acquisition, rental and maintenance. In this context, enabling cordless or non-wired RSs with an alternative source of power, such as through using a solar power source, has been proved efficient in some deployment scenarios. Alternatively, deploying an AP without an alternative power supply which is otherwise required to ensure robustness to power outages also yields a substantial reduction in the deployment cost. In both cases, the ability of an AP or RS to substantially reduce its power consumption during inactivity or idle periods is desirable.
Various forms of power saving operations such as sleep and idle modes are known for nodes in IEEE Std. 802.11, and in portable devices cellular wireless standards to improve battery life of user equipment (UE), access terminals (AT), or other portable devices. Looking first at the former example, the concept of power efficient operation for network nodes is known in IEEE Std. 802.11 to enable power efficient forwarding in a mesh Wi-Fi network. The known power save (PS) mode supported in 802.11 can be seen as a form of active sleep mode where a wireless node stays on at a predefined regular schedule to receive, transmit and/or forward traffic. The 802.11 PS form of power save can potentially apply to any node and facilitates mesh operation where battery powered devices can be used to forward traffic, and thus could conceivably be applied to cellular APs and RSs (or ATs in peer-to-peer mode). It is noted, however, that PS mode is an example of an active sleep mode, and its duty cycle when active is noticeably larger compared to the duty cycle of idle mode of cellular systems and thus would not offer significant power savings.
In wireless cellular systems, user equipment (UE), ATs, or other portable equipment feature power save operations are “idle mode” and various forms of active “sleep mode.” In an optimized idle mode, for example, an average duty cycle of AT activity is typically within a fraction of a percent of the normal duty cycle. An AT in idle mode wakes up periodically to monitor paging channel, track a potential serving AP as well as candidate serving APs and eventually switch the candidate serving AP (i.e. perform idle handoff) and register in the case of paging zone change. Additional operations may include updating AP parameters as needed to perform initial access etc. A regular wake-up cycle is usually tied to the paging cycle which takes values between approximately 500 ms and a few seconds depending on device type and anticipated application. Idle mode design in cellular systems assumes that APs are always active and provide regular pilot transmission with a fixed periodicity of tens of milliseconds or less as well as opportunity for access or hand-in of an AT. While this assumption may substantially facilitate idle mode design at the AT, it prevents power efficient operation of APs.
Application of the above-discussed idle or sleep modes to node devices such as serving APs, RSs or even serving ATs in a peer-to-peer situation, however, is not known and strict application of known techniques to APs or RSs would not result in efficient and significant power savings, nor even be able to provide operation consistent with requirements of the AP or RS. Accordingly, it would be beneficial to provide techniques to achieve an efficient implementation of idle mode operations in an AP or RS (or AT operating as serving equipment in a peer-to-peer mode) to engender power savings.